It is generally known that vas deferens is a suitable site for contraceptive intervention in the male. Vasectomy is a well established method of male contraception. In such a method, the vas deferens is cut and tied so as to prevent the sperms from flowing in the forward direction, and the sperms accumulate in the epididymes. Due to the presence of such sperms, the body generates enhanced antibodies to destroy the accumulated sperms. A disadvantage associated with such a method is that even after rejoining of the vas deferens, fertility is low as the body maintains the high level of antibodies and continues to destroy the sperms. Yet another disadvantage is that such a method requires surgery.
Besides vasectomy, reversible occlusion methods are also known in the art, which also prevents a forward flow of the sperm. One such occlusion method consists in implantating a reversible occlusion device for providing a blockage of the flow of sperms in the vas deferens. The device has a regulator knob outside of the vas deferens but inside the serotum. The regulator knob is normally operated by only a trained medical assistant. A disadvantage associated with such a device is that it also requires a surgery so as to allow an implantation. Another disadvantage is that during blockage, the body once again develops an enhanced level of antibodies to the sperms, which persists even upon opening or removal of the device. Yet another disadvantage arises in the instance where the closure may not be perfect resulting in a flow of sperms, though limited only quantitatively, but which cannot then be destroyed.
Yet another occlusion method known in the art consists in injecting polyurethane at a high pressure into the vas deferens. The polymer is further polymerized in the vas deferens by also introducing an initiator by which polyurethane sets into a solid plug to prevent a flow of the sperms in the forward direction. An additional disadvantage associated with such a method besides those described hereinabove with respect to the occlusion methods is that a back pressure is developed in the epididymes, which also reduces fertility.
Work by the present inventors on injecting styrene maleic anhydride in a solvent vehicle of dimethyl sulphoxide has been reported in Contraception 1993 : 48 October. Such a publication discloses in vitro pH-lowering effect but does not discuss the effect on the fertilizing ability of sperms.